A network administrator finds that access to a secure server using HTTPS is failing due to a firewall issue. Which port should be opened to solve the problem?

To facilitate secure access to a server using HTTPS, it is vital to ensure that the appropriate network port is open on the firewall. HTTPS, which stands for Hypertext Transfer Protocol Secure, operates over port 443. This port is specifically designated for secure web traffic, allowing encrypted communication between clients and servers.

Opening port 443 on the firewall allows traffic that is utilizing SSL/TLS encryption to pass through, ensuring that users can access the secure server without interruption. This is crucial for maintaining the confidentiality and integrity of the data being transmitted over the network.

In contrast, other ports such as 80 are typically used for HTTP traffic, which is not secure. Port 21 is associated with FTP (File Transfer Protocol), and port 25 is designated for SMTP (Simple Mail Transfer Protocol). Therefore, these ports do not relate to providing secure access to web services and would not resolve the issue at hand. Focused on enabling secure connections, the administrator must prioritize the correct protocol and corresponding port to ensure seamless server access.